USRP2 - BasicTX first Nyquist zone frequencies


#1

Hello,

I read in faq that the bigger frequency of the first Nyquist zone of
USRP2 is about 170 MHz, using a BasicTX daughter board.
My USRP2 couldn’t get more than 50 MHz with this daughter board.

I’m using 9939 firmware revision.

Somebody observed the same problem with usrp2?
There is a way to fix it?

Thanks


Ronaldo A. Viera Nunez
Acadêmico/Engenharia Elétrica
Universidade Federal de Santa Maria

Santa Maria - RS - Brasil


#2

On Mon, Mar 16, 2009 at 10:05:28AM -0300, Ronaldo N. wrote:

Thanks

I’m not sure where you found the 170 MHz number, or where it may have
come from, but the USRP2 DACS run at 100 MS/s. With the Basic Tx
50 MHz is what you would expect to see as the edge of the first
Nyquist zone.

Eric


#3

Hi Eric,

i felt like you when I read it, but take a look here
(http://gnuradio.org/trac/wiki/USRP2GenFAQ) :

"With Basic TX board, USRP1 can generate maximum of 44 MHz frequency,
What USRP2 is capable of ?

44 MHz is the highest frequency in the first Nyquist zone on the USRP1.
Much higher frequencies can be used in the higher zones. The USRP2
takes 100 MS/s rates and interpolates up to 400 MS/s. Direct
frequencies up to ~170 MHz should be usable. "

Maybe I interpreted wrong… Be free to correct me…

Regards,

Ronaldo

2009/3/16 Eric B. removed_email_address@domain.invalid:

There is a way to fix it?

Thanks

I’m not sure where you found the 170 MHz number, or where it may have
come from, but the USRP2 DACS run at 100 MS/s. With the Basic Tx
50 MHz is what you would expect to see as the edge of the first
Nyquist zone.

Eric


Ronaldo A. Viera Nunez
Acadêmico/Engenharia Elétrica
Universidade Federal de Santa Maria

Santa Maria - RS - Brasil


#4

Thanks Eric,

I will try your suggestion, if I get it I will share the information
with the community.

Regards,

Ronaldo

2009/3/16 Eric B. removed_email_address@domain.invalid:

Much higher frequencies can be used in the higher zones. The USRP2
The firware sets up the DAC (AD9777) in the interpolate by 4, no

I’m not sure where you found the 170 MHz number, or where it may have
come from, but the USRP2 DACS run at 100 MS/s. With the Basic Tx
50 MHz is what you would expect to see as the edge of the first
Nyquist zone.

Eric


Ronaldo A. Viera Nunez
Acadêmico/Engenharia Elétrica
Universidade Federal de Santa Maria

Santa Maria - RS - Brasil


#5

On Mon, Mar 16, 2009 at 07:04:11PM -0300, Ronaldo N. wrote:

takes 100 MS/s rates and interpolates up to 400 MS/s. Direct
frequencies up to ~170 MHz should be usable. "

Maybe I interpreted wrong… Be free to correct me…

Regards,
Ronaldo

Ronaldo,

The firware sets up the DAC (AD9777) in the interpolate by 4, no
modulation mode. Given that, the remarks about 50 MHz apply. Feel
free to experiment with the on-chip modulator and let us know how it
works out. FYI, the code that initializes the DAC is in u2_init.c

Eric


#6

On Tue, Mar 17, 2009 at 01:08:54PM -0300, Ronaldo N. wrote:

Thanks Eric,

I will try your suggestion, if I get it I will share the information
with the community.

Regards,
Ronaldo

Thanks!

Eric


#7

Hi Eric,

I solved the problem using your suggestion.

I changed the line 76 at u2_init.c:

from: ad9777_write_reg(1, R1_INTERP_4X | R1_REAL_MIX);
to: ad9777_write_reg(1, 0xB0 | R1_REAL_MIX);

Then, I was able to tx frequencies higher than 50 MHz - [50,100] MHz.

Thanks a lot! :smiley: